Determination of pentachlorophenol at carbon nanotubes modified electrode incorporated with beta-cyclodextrin

A facile and reliable electrochemical technique at beta-cyclodextrin incorporated carbon nanotubes modified glassy carbon electrode (beta-CD/CNTs/GCE) was proposed for determination of pentachlorophenol (PCP). The electrochemical behavior of PCP at the beta-CD/CNTs/GCE was investigated by cyclic voltammetry and linear sweep voltammetry. The beta-CD/CNTs/GCE showed good analytical performance characteristics in electrocatalytic oxidation of PCP, compared with the simple carbon nanotube modified electrode (CNTs/GCE) and bare glassy carbon electrode (GCE). After accumulation for 5 min on beta-CD/CNTs/GCE, the peak current increased linearly with the concentration of PCP in the range from 8.0 x 10(-7) to 1.04 x 10(-5) mol/L. The detection limit was 4.0 x 10(-8) mol/L at 3 sigma level. The proposed electrode presented good repeatability for the determination of PCP in artificial wastewater, and the recovery was 97%-103%. This modified electrode combined the advantages of carbon nanotubes and supramolecular cyclodextrin, leading to new capabilities for electrochemical detection of PCP.     

Electrocatalytic detection of NADH and glycerol by NAD(+)-modified carbon electrodes

The electrochemical oxidation of the adenine moiety in NAD+ and other adenine nucleotides at carbon paste electrodes gives rise to redox-active products which strongly adsorb on the electrode surface. Carbon paste electrodes modified with the oxidation products of NAD+ show excellent electrocatalytic activity toward NADH oxidation, reducing its overpotential by about 400 mV. The rate constant for the catalytic oxidation of NADH, determined by rotating disk electrode measurements and extrapolation to zero concentration of NADH, was found to be 2.5 x 10(5) M-1 s-1. The catalytic oxidation current allows the amperometric detection of NADH at an applied potential of +50 mV (Ag/AgCl) with a detection limit of 4.0 x 10(-7) M and linear response up to 1.0 x 10(-5) M NADH. These modified electrodes can be used as amperometric transducers in the design of biosensors based on coupled dehydrogenase enzymes and, in fact, we have designed an amperometric biosensor for glycerol based on the glycerol dehydrogenase (GlDH) system. The enzyme GlDH and its cofactor NAD+ were co-immobilized in a carbon paste electrode using an electropolymerized layer of nonconducting poly(o-phenylenediamine) (PPD). After partial oxidation of the immobilized NAD+, the modified electrode allows the amperometric detection of the NADH enzymatically obtained at applied potential above 0 V (Ag/AgCl). The resulting biosensor shows a fast and linear response to glycerol within the concentration range of 1.0 x 10(-6)-1.0 x 10(-4) M with a detection limit of 4.3 x 10(-7) M. The amperometric response remains stable for at least 3 days. The biosensor was applied to the determination of glycerol in a plant-extract syrup, with results in good agreement with those for the standard spectrophotometric method.     

Synthesis and characterization of processable multi-walled carbon nanotubes-sulfonated polydiphenylamine graft copolymers

Water soluble and processable nanocomposites composed of multi-walled carbon nanotubes (MWNTs) and poly(diphenylamine sulfonic acid) (PDPASA) are synthesized and characterized. Two types of methodologies are adopted. MWNTs are covalently functionalized with 2,5-diaminobenzene sulfonic acid (DABSA) and further in situ polymerized with diphenylamine-4-sulfonic acid (DPASA). This results in the formation of nanocomposites, MWNT(DABSA)-g-PDPASA, in which PDPASA is presented as the graft chains onto MWNTs. In another approach, DPASA is in situ polymerized in presence of unfunctionalized MWNTs, results in a nanocomposite in which MWNTs are present as entrapped mass in PDPASA matrix. Both nanocomposites are found to be water soluble and can form free standing films. The conductivity of MWNT(DABSA)-g-PDPASA and MWNT/PDPASA is found to be 1.25 mS x cm(-1) and 0.65 mS x cm(-1), respectively, which is higher than that of pristine PDPASA (0.25 x 10(-5) S x cm(-1)). The nanocomposites are characterized for their structure, morphology, optical and thermal properties.     

Chemical reversibility and stable low-potential NADH detection with nonconventional conducting polymer nanotubule modified glassy carbon electrodes

Studies of the oxidation of beta-nicotinamide adenine dinucleotide (NADH) at glassy carbon (GCEs) electrode surfaces, modified with nonconventional conducting polymer nanotubules, are reported. In contrast to the situation with conventional carbon electrodes, chemical reversibility of the NADH oxidation reaction was achieved by means of poly(1,2-diaminobenzene) conducting nanotubule coatings. A Delta E(p) of 425 mV (vs Ag/AgCl; pH 7.0) was observed. The NADH amperometric response of the conducting nanotubule modified GCEs was shown to be extremely stable, with 98% of the initial response remaining after 48 h of stirring in the presence of 1 x 10(-4) M NADH solutions (compared to 14% at the poly(1,2-diaminobenzene) modified GCEs). The nonconventional conducting polymer nanotubule-coated electrodes, when tested in amperometric mode for NADH electrochemical oxidation at an applied potential of 450 mV, showed a sensitivity of 99 nA/mM, an operational stability for 2 days, a storage stability of 2 weeks at 4 degrees C, a linearity from 5 x 10(-5) to 1 x 10(-3) M, and good NADH chemical reversibility, all of which make them useful tools for dehydrogenase enzyme probe assembly.     

Quantitative counting of single fluorescent molecules by combined electrochemical adsorption accumulation and total internal reflection fluorescence microscopy

We developed an ultrasensitive quantitative single-molecule imaging method for fluorescent molecules using a combination of electrochemical adsorption accumulation and total internal reflection fluorescence microscopy (TIRFM). We chose rhodamine 6G (R6G, fluorescence dye) or goat anti-rat IgG(H+L) (IgG(H+L)-488), a protein labeled by Alexa Fluor 488 or DNA labeled by 6- CR6G (DNA-R6G) as the model molecules. The fluorescent molecules were accumulated on a light transparent indium tin oxide (ITO) conductive microscope coverslip using electrochemical adsorption in a stirred solution. Then, images of the fluorescent molecules accumulated on the ITO coverslip sized 40 x 40 microm were acquired using an objective-type TIRFM instrument coupled with a high-sensitivity electron multiplying charge-coupled device. One hundred images of the fluorescent molecules accumulated on the coverslip were taken consecutively, one by one, by moving the coverslip with the aid of a three-dimensional positioner. Finally, we counted the number of fluorescent spots corresponding to single fluorescent molecules on the images. The linear relationships between the number of fluorescent molecules and the concentration were obtained in the range of 5 x 10(-15) to 5 x 10(-12) mol/L for R6G, 3 x 10(-15) to 2 x 10(-12) mol/L for IgG(H+L)-488, and 3 x 10(-15) to 2 x 10(-12) mol/L for DNA-R6G.     

Triiodide PVC membrane electrodes based on charge-transfer complexes

Three new electrodes were prepared by incorporating two different charge-transfer complexes and amino crown ether into plasticized PVC membranes. The electrodes showed Nernstian response to triiodide ion over the activity range from 1.0 x 10(-5) to 1.0 x 10(-1) mol x L(-1) with detection limits at approximately 1.0 x 10(-6) mol x L(-1). The resulting electrodes have fast response times (20-30 s) and good stabilities (4 months) and can be used over a wide pH range of 2.5-9.0. The proposed electrodes exhibit anti-Hofmeister behavior with excellent selectivity toward triiodide ion against a wide range of common interferences. Comparative study suggests that amino (aza) crown ether alone or in the form of a charge-transfer complex with iodine, as an ionophore in a PVC liquid membrane, is sensitive to triiodide ion. The electrodes were used as indicator electrodes in potentiometric titration of triiodide ion against thiosulfate ion.     

Influence of surface electrode on luminescent properties of nanocrystalline silicon electroluminescent device

We describe the electrical and luminescence properties of nanocrystalline silicon (nc-Si) based red electroluminescent (EL) devices using an indium tin oxide (ITO) and/or gold (Au) films as a surface electrode, and the variation in the transmittance and resistivity of two electrodes with various film thicknesses. The increase in the film thickness from 50 to 200 nm of the ITO electrode led to the lowering of resistivity from 2.0 x 10(-3) to 9.1 x 10(-4) omega cm and almost the same value (83-92%) of transmittance in the red region. On the other hand, the Au electrode was lowered the resistivity from 1.8 x 10(-4) to 1.6 x 10(-5) omega cm and the transmittance in the red region from 42 to 1.8% with increasing the film thickness from 10 to 80 nm. Moreover, the red luminescence from the EL devices using the ITO and/or Au electrodes having thickness of 200 and 10 nm, respectively, obtained by applying the direct current forward voltage above 4.5 and 2.5 V and/or by flowing the forward current density above 53 and 38 mA/cm2, respectively. However, the luminescence intensity of EL device with the ITO electrode strengthened more than about one order of magnitude in comparison to that of the EL device with the Au electrode. This was due to the high value of transmittance in the red region of the ITO electrode. We suggest that the ITO electrode is an optimum surface electrode for the realization of nc-Si based EL device with the high brightness.     

Electrochemical detection of low concentration chloropropanol using silver nanowire array electrodes in aqueous media

In this paper, we report a facile method to fabricate silver nanowire array electrodes (SNAE) with ultra-high detection sensitivity to chloropropanol in the aqueous solution. Silver nanowire arrays were assembled in conventional anodic alumina membranes (AAM) by electrochemical deposition. Subsequently, silver nanowire arrays with an aspect ratio of 5 approximately 6 were deposited on the bottom of AAM. After a complete removal of the AAM , the grown arrays were used as working electrodes in a three-electrode cell. The electrochemical activity of SNAE was tested in the 0.1 mol/L NaClO4 aqueous solution using chloropropanol as analyte by a cyclic voltammetry method. The results show that SNAE display a distinct reduction peak at -1.011 V (vs. SCE) for chloropropanol and the linear dependencies of current on chloropropanol concentration were obtained within the concentration range 1.8 x 10(-7) approximately 2 x 10(-6) mol/L. The detection limit of chloropropanol was 10(-9) mol/L, which is significantly lower than that of their bulk counterparts. In short, SNAE show great potential in the determination of trace chloropropanol.     

Synthesis,characteristic, and flammability of modified carbon nanotube/poly(ethylene-<Emphasis Type="Italic">co</Emphasis>-vinyl acetate) nanocomposites containing phosphorus and silicon

A novel flame retardant containing phosphorus–silicon, spirocyclic pentaerythritol bisphosphorate disphosphorylchloride/9,10-dihydro-9-oxa-10-phosphaphanthrene-10-oxide/vinyl methyl dimethoxysilane (SPDV), has been used to modify multiwalled carbon nanotubes (MWNTs) and the m-MWNTs (MWNTs-g-SPDV) was obtained by the covalent grafting of SPDV onto the surfaces of MWNTs. And then the according poly(ethylene-co-vinyl acetate) nanocomposites were prepared via melt blending. Transmission electron microscopy (TEM) results showed that a core–shell nanostructure with MWNTs as the hard core and SPDV as the soft shell was formed, and the resultant m-MWNTs can achieve better dispersion than pristine MWNTs in EVM matrix. Cone calorimeter results showed that better flame retardancy was obtained for EVM/m-MWNTs nanocomposites. Mechanical measurements showed that the Young’s modulus increases due to the presence of MWNTs or m-MWNTs. The flammability and mechanical properties of the nanocomposites are strongly dependent on the dispersion state of nanotubes.     

Effect of pyrene-modified multiwalled carbon nanotubes on the properties of epoxy composites

The block polymer of poly(styrene-b-pyrene) (PS-b-PAH) containing pyrene units was successfully applied on the surface of multiwalled carbon nanotubes (MWNTs) and the properties of nanocomposites were enhanced. The morphology of the modified MWNTs was characterized by transmission electron microscopy (TEM), and the results showed that PS-b-PAH helped effectively the MWNTs to disperse well in epoxy matrices, and these dispersed MWNTs were stabilized by the pyrene modifier. The mechanical properties of the composites, such as impact toughness and flexural strength, and the electrical conductivity of the nanocomposites, are improved significantly after the treatment of the MWNTs using PS-b-PAH. The results show that the mechanical and electrical properties of the modified MWNTs/epoxy composites with PS-b-PAH are obviously superior to those of pristine MWNTs/epoxy composites. The enhanced interfacial interactions lead to good dispersion of MWNTs in epoxy matrices, thus enhancing the mechanical and electrical properties of the nanocomposites.     

Preparation and properties of the polyimide/multi-walled carbon nanotubes (MWNTs) nanocomposites

The polyimide/multi-walled carbon nanotubes (MWNTs) nanocomposite films were prepared by mixing of poly(amic acid) (PAA) solution and MWNTs/DMAc suspension follow by mixture casting, evaporation and thermal imidization. To increase the chemical compatibility between polyimide matrix and MWNTs, MWNTs were modified with mixed strong acid. The results show that the dispersion of the MWNTs is improved greatly in the polyimide matrix after acid modification. The modified MWNTs are dispersed homogeneously in the polyimide matrix while the structure of the polyimide and MWNTs structures is stable in the preparation process. With the incorporation of MWNTs, the mechanical properties of the resultant nanocomposite films were greatly improved due to the strong interfacial interaction between the modified MWNTs and the polyimide matrix. The thermal stability of the nanocomposites was lower a little than pure polyimide because of the drop of thermostability of MWNTs through acid-treatment. The electrical conductivity and the dielectric constant of the nanocomposites were also having sharp increase, which is favorable for practical use in anti-static materials and embedded capacitors.     

Influence of multi-walled carbon nanotubes on electrochemical performance of transparent graphene electrodes

In this work, carbon-carbon nanocomposites as transparent electrodes were prepared by a chemical reduction of graphite oxide (GO) and multi-walled carbon nanotubes (MWNTs). The electric, optical, and electrochemical properties of graphene-MWNT nanocomposites (G-MCs) were investigated as a function of the MWNT content. It was found that chemically bonded G-MCs were successfully formed with a reduction of the functional groups of the GO and acid-treated MWNTs, resulting in the conjugation of 1D MWNTs onto a 2D graphene surface. The electrical conductivity of the graphene was significantly enhanced by introducing the MWNTs. In addition, the G-MCs showed improved current density and high efficiency compared with graphene alone. This indicated that the improved electrochemical performance of the G-MCs can be attributed to the increase in the activity and electrical conductivity enhanced by π-π interaction between graphene and MWNTs.     

A method for the fabrication of low-noise carbon fiber nanoelectrodes

A new and facile method has been developed for the fabrication of low-noise carbon fiber microelectrodes (CFMEs) and carbon fiber nanoelectrodes (CFNEs). The carbon fiber was flame-fuse sealed in the tip of the glass capillary. The CFMEs were made by cutting the protruding carbon fiber to the desired length, and the CFNEs were achieved by etching the protruding carbon on the flame to form a nanometer-scale tip. The tip of CFNEs can be controlled within the range from 100 to 300 nm. Thus, no epoxy wax was involved in the CFMEs and CFNEs. The experimental results of inspecting CFMEs and CFNEs by scanning electron microscopy demonstrated that the surface of the electrodes and the glass/fiber interface are very smooth. Therefore, the noise caused by the glass/fiber of these electrodes is much lower than that of the electrodes fabricated conventionlly. The electrodes were characterized by ferricyanide, catecholamine (dopamine,DA), norepinephrine (NE), and epinephrine (E)) and 5-hydroxytryptamine (5-HT) neurotransmitters using CV, LSV, DPV, and FSCV. The results showed that the CFMEs and CFNEs have very excellent electrochemical behavior and high sensitivity. The CV and DPV detection limits of DA, NE, and E are 7.6 x 10(-8), 7.0 x 10(-8), and 5.0 x 10(-8) mol/L, and the DPV detection limits of DA, NE, and E are 4.0 x 10(-8), 1.0 x 10(-7), and 2.2 x 10(-7) mol/L, respectively. This experiment offers a new and facile method for the fabrication of CFMEs and CFNEs of very high sensitivity and low noise.     

Lipophilic lanthanide tris(beta-diketonate) complexes as an ionophore for Cl- anion-selective electrodes

A series of novel anion-selective electrodes were developed by incorporating lipophilic lanthanide tris(beta-diketonates) into plasticized poly(vinyl chloride) membranes. The new electrodes exhibited high selectivity toward Cl(-) anion in the concentration range of Cl(-) anion between 1.0 x 10(-5) and 1.0 x 10(-1) mol/L with near-Nernstian slopes and practically low detection limits. They offered non-Hofmeister anion selectivity, and interestingly discriminated Cl(-) anion from NO(3)(-), ClO(4)(-), and other anions. Since the employed lanthanide tris(beta-diketonates) were confirmed to form 1:1 highly coordinated complexes with Cl(-) anion, the observed high selectivity for Cl(-) anion was attributed to the characteristics of lanthanide coordination chemistry. All the prepared sensors worked well at neutral pH with quite short response time, <30 s, and could be used for longer than four months without any significant divergence in performance.     

Studies on preparation and properties of the multi-walled carbon nanotubes (MWNTs)/epoxy nanocomposites

The MWNTs were coated with polyaniline (PANI) by in situ chemical oxidation polymerization method. FTIR spectroscopy, scanning electron microscope (SEM) and X-ray diffraction (XRD) indicated that the MWNTs were coated with PANI. The MWNTs/epoxy nanocomposites were fabricated by using the solution blending method. Differential scanning calorimetry (DSC), tensile testing, HP 4294A impedance analyzer and SEM were used to investigate the properties of the nanocomposites. The results showed that the modified carbon nanotubes were well dispersed in the polymer matrix. The nanocomposites have enhancements in mechanical, thermal and dielectric properties compare with the neat epoxy resin. The nanocomposites were proven to be a good polymer dielectric material.     

On-column coaxial flow chemiluminescence detection for underivatized amino acids by pressurized capillary electrochromatography using a monolithic column

A new method for pressurized capillary electrochromatography (pCEC) coupling with chemiluminescence (CL) detection using a modified on-column coaxial flow detection interface was developed. To evaluate the feasibility and reliability of the experimental setup, the typical CL compounds luminol and isoluminol were separated and detected by using this pCEC-CL system. A detailed investigation of CL detection interface and postcolumn CL reagent flow rate parameters was described. The excellent resolution and detection sensitivity was achieved by using 3-microm ODS-C18 packed column with 30% ACN (v/v), 5 mmol/L phosphate buffer (pH 8.0). Moreover, with the presence of Co(II) (1.0 x 10(-4) mol/L) in the mobile phase, the linear range of the concentration for luminol was 2.0 x 10(-9)-2.0 x 10(-6) mol/L with a detection limit (S/N = 3) of 2.0 x 10(-10) mol/L, and 2.5 x 10(4) theoretical plates was achieved. In addition, separation and detection of the underivatized amino acids (l-threonine and l-tyrosine) were accomplished by using a polymerized monolithic column based on the principle of the luminol-H2O2-Cu(II)-amino acid CL system. Under the optimum conditions, the mixture of amino acids was efficiently separated with satisfactory results.     

Electrocatalysis of NADH oxidation with an electropolymerized film of 1,4-bis(3,4-dihydroxyphenyl)-2,3-dimethylbutane

The oxidation of 1,4-bis(3,4-dihydroxyphenyl)-2,3-dimethylbutane, known also as nordihydroguaiaretic acid, on a glassy carbon electrode anodically pretreated in KCl solution gives rise to a stabile redox-active polymer containing the o-quinone moiety. The redox response of the modified electrode is typical for a surface-immobilized species. The modifier thickness can be easy controlled by a number of potential cycles applied during electropolymerization, and a surface coverage up to 1.1 x 10(-9) mol cm(-2) can be achieved. The film exhibits catalytic activity toward NADH oxidation. Characteristic kinetic constants for the mediated oxidation of NADH were derived from rotating disk experiments performed in phosphate or Tris/acetate buffers. The effects of film thickness, solution pH, and the presence of Mg2+ cation on the catalytic efficiency of the modified electrode were discussed and compared with literature data concerning related systems.     

氮掺杂多孔碳负载铜钴纳米复合材料的制备及其电催化性能EI北大核心CSCD

先以ZIF-8作为前驱体采用简单的高温炭化法制备出氮掺杂多孔碳纳米多面体(NPC),再通过一步化学还原法将铜和钴颗粒负载到多孔碳上,成功制备出Cu@Co/NPC纳米复合材料。运用X射线粉末衍射仪、透射电子显微镜和X射线光电子能谱等手段对复合材料进行表征,将该复合材料修饰到玻碳电极表面上,研究其对肼的电化学响应。结果表明,Cu@Co/NPC纳米复合材料发挥出协同作用,从而对肼展现出比单一组分修饰电极更优异的电催化作用。在优化的实验条件下,复合材料修饰电极与肼的浓度在5~1850μmol/L范围内呈良好的线性关系,检测限达0.08μmol/L。此外,该复合材料修饰电极测定肼的稳定性、重现性以及选择性均较好,已被成功用于环境水样中肼的检测,结果令人满意。     

Amperometric determination of hydrogen peroxide by functionalized carbon nanotubes through EDC/NHS coupling chemistry

The electrochemistry of the redox mediator Toluidine blue (TB) which was covalently linked to the carboxyl group of the multiwalled carbon nanotubes (MWNTs) by coupling reactions, in which N-hydroxysuccinimide was used to assist 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride catalyzed amidation reaction is described. The results from cyclic voltammetry (CV) and amperometry suggested that the redox mediator is linked to the surface of the MWNTs and the nanotubes showed an obvious promotion for the direct electron-transfer between the redox mediator and the electrode. A couple of well-defined redox peak of TB was observed in a phosphate buffer solution (pH 7.0). The redox mediator immobilized to MWNTs exhibits remarkable electrocatalytic activity for the reduction of hydrogen peroxide (H2O2). The analytical applicability of the modified electrode for the determination of hydrogen peroxide was examined. A linear response in the concentration range of 6.8 x 10(-7)-3.4 x 10(-2) M (r = 0.9958) was obtained with detection limit of 3.4 x 10(-7) M for the determination of hydrogen peroxide. The modified electrode has advantages of being highly stable, sensitive, ease of construction and use.     

Preparation and characterization of aligned carbon nanotube-ruthenium oxide nanocomposites for supercapacitors

A novel type of ruthenium oxide (RuO(2))-modified multi-walled carbon nanotube (MWNT) nanocomposite electrode (RuO(2)/MWNT) for supercapacitors has been prepared. The nanocomposites were formed by depositing Ru by magnetic-sputtering in an Ar/O(2) atmosphere onto MWNTs, which were synthesized on Ta plates by chemical vapor deposition. Cyclic voltammetry, chronopotentiometry, and electrochemical impedance measurements were applied to investigate the performance of the RuO(2)/MWNT nanocomposite electrodes. The capacitance of the MWNT electrodes in 1.0 M H(2)SO(4) is significantly increased from 0.35 to 16.94 mF cm(-2) by modification with RuO(2). The RuO(2) film on the surface of the nanotubes is composed of small crystal grains with tilted bundle-like microstructures, as observed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The results demonstrate a promising route to prepare RuO(2)/MWNT-based double-layer supercapacitors.